Deflation control valve

ABSTRACT

A deflation control valve that automatically varies the rate of air flow through said control valve to provide a constant but adjustable rate of change of pressure during the deflation or exhaust of gas held in a closed pressurisable vessel to which said valve is connectable comprising a valve body having a passage communicatable with said pressurisable vessel, said valve body defining a valve chamber communicating with said passage in which a flexible diaphragm is provided partially or substantially closing said valve chamber, said diaphragm being in sealing abutment with a seat in said valve housing around the periphery of said diaphragm, and forming on the opposing side a part of an exhaust chamber, said diaphragm, in use, being, on the valve chamber side subject to the gas pressure in said pressurisable vessel and, on the opposing side, subject to the gas pressure in the exhaust chamber, which may be atmospheric pressure, and said diaphragm having an aperture or port extending therethrough, and said diaphragm on one side being in communication with said valve chamber and, on the opposite side, being in communication with said exhaust chamber or atmosphere and being closeable or partially closeable by a displaceable closure disc, plate or platen which is releasably held in the closing position against said diaphragm and covering said port by an operable, controllable or adjustable release means, which by adjusting said release means to open and closed positions or intermediate positions, controls the rate at which gas flows through the valve, gas passing from the valve chamber through the port in the diaphragm and between the face of the closure disc and diaphragm to exhaust or atmosphere to allow the pressure of the pressure chamber to drop in a controlled manner.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to UK 0610300.6 filed May 24, 2006 andUK 0704186.6 filed Mar. 5, 2007, which applications are herebyincorporated by reference in their entirety.

The present invention relates to a deflation control valve for asphygmomanometer. The valve of the present application is a deflationcontrol valve particularly but not exclusively for use with our latestsphygmomanometer monitor (which is sold under the name “Greenlight”)which is to replace mercury and Bourden manometers and which is anaccurate: self calibrating electronic manometer. Mercury is no longeracceptable for blood pressure measurement and Bourden gauges, thoughcheap and small: lose calibration fairly quickly. Automaticsphygmomanometers do not use the auscultatory technique and clinicianshave concerns about their accuracy and appropriateness. Our newelectronic manometer provides an effective solution. However, our newmonitor demands more from the deflation control valve. The monitorincorporates a deflation rate indicator. Standards set an acceptabledeflation rate (2 mmHglsec) for the measurement of blood pressure in thesystolic and diastolic pressure zones and this deflation rate isindicated on our monitor. The valve has to be accurate and controllableenough to allow clinicians to adjust the deflation rate easily to thecorrect value. This is made more difficult as the volume of air held inthe electronic monitor is small compared to that held in a mercurysphygmomanometer and the valve has to be able to control smaller airflow rates for a given deflation rate than when used with a mercurysphygmomanometer.

There are two types of deflation valve commonly in use, needle valvesand sleeve/piston valves. Needle valves are the most widespread; they donot give sufficiently precise control of the deflation rate at such lowair flow to be able to set it easily to 2 mm Hg/sec. Sleeve valves arebetter, but neither type compensate for reducing flow rate as the cuffpressure drops or give a tactile indication of the setting zone.

After development of the valve of the present invention, there wasdiscovered U.S. Pat. No. 4,198,031 of Gulf & Western Industries whichdiscloses an automatic air deflation valve for use with asphygmomanometer and comprising a housing having an air flow channelextending through the longitudinal extent thereof and at least one airdeflation port extending outwardly from said channel. The port includesa deformable diaphragm, which may be two part, sealingly supported onlyon its outer edges and otherwise without restraint and having a centralaperture extending through the thickness thereof. The diaphragm andaperture are adapted to deform in accordance with the air pressureapplied against it from said channel to automatically adjust the sizeand shape of said aperture, thus producing a constant air deflation ratetherethrough. The valve has an override (dump) valve for fast deflation;it is not adjustable for different deflation rates, cuff or arm sizes.The valve cannot be closed, has no manual control or adjustment andappears to be designed for use on automated devices.

Features sought in an improved deflation control valve includes any ofthe following considerations:

-   -   1. The valve has to be sensitive and accurate enough to set the        deflation rate correctly.    -   2. The valve needs to be able maintain the deflation rate        consistently as the pressure in the cuff and monitor is        dropping. The valve should compensate for the reducing pressure        in the measurement zones, keeping the deflation rate as constant        as possible and allowing the clinician to concentrate on the        diagnosis rather than the manipulation of the valve.    -   3. Clinicians need to be able to find the correct valve position        quickly at the systolic and diastolic pressures and to increase        airflow easily outside these pressure zones so that the cuff        remains inflated on a patient's arm for as short a period as        possible. Some tactile features that help the clinician find the        operating zone of the valve will be helpful.

4. The relationship between the angular position of the knob and thedeflation rate should be perceived by the clinician as proportional andeasily controlled. The rotation of the knob to vary the deflation ratefrom 2 mm Hg per second to say 8 mm Hg per second for the smallest cuffsize should ideally be similar to that needed to vary the deflation rateof the largest cuff size over the same range (though it is likely thatthe absolute position of the knob to achieve a given flow rate will varyaccording to cuff size). The valve should also be able to be opened andclosed fully quickly—the knob rotation from the start or end of theadjustment zone to the fully open or fully closed position should beappropriate.

These requirements indicate that the relationship between the angularrotation of the knob and the position of the platen is unlikely to beeither linear or directly proportional.

-   -   5. The valve should connect to other components in the system        with a push taper connection.    -   6. The valve, though precise and accurate must be robust in use.    -   7. The valve should be as small as possible.

A number of different methods of controlling air flow were considered inthe evolution of the present invention including accurate needle valvescontrolled by a more precise mechanism, improved sleeve valves and facevalves. Of the types considered, it was discovered face valves offered away of compensating flow rate for diminishing pressure in the cuff andkeeping a steady deflation rate without continual adjustment of thevalve. They also seemed effective at controlling low air flow rates. Anumber of test rigs were made to learn more about the behavior of facevalves.

According to the present invention there is provided a deflation controlvalve according to claim 1. Also according to another aspect of theinvention there is provided a deflation control valve in the form of aface valve for a sphygmomanometer comprising a valve body having a firstoutlet passage connectable to be communicatable with a pressurisabletube connected to a cuff of a sphygmomanometer and an inlet passageconnectable to a rubber bulb pump or like inflation means, said valvebody defining a valve chamber in which a flexible diaphragm is providedpartially or substantially closing the chamber and said diaphragm havinga deflation, air-flow passage which on one side of the diaphragm is incommunication with said inlet and outlet passage and, on the oppositeside of the diaphragm, is in communication with an exhaust outlet oratmosphere and is closeable or partially closeable during inflation by adisplaceable closure disc, plate or platen which is releasably held inthe closing position against said passage by a manually operable,controllable or adjustable release means.

The flexible diaphragm is preferably resilient.

Preferably the manually operable release means is a reversibly rotatableand axially displaceable control knob bearable on the platen, or such isa non-axially displaceable rotary knob with cam and lever means forreversibly urging the platen into a closing position. Preferably thedisplacement means associated with the knob (such as a screw thread ortapered cam surface) is geared such that the movement is amplified andthus greater movement of the knob enables a smaller movement of the discor platen.

Preferably the platen and/or diaphragm has an air escape passage ormeans which varies in cross-section as the pressure under the diaphragmis reduced and which can be controlled by lifting and lowering theplaten. It is alternately or additionally possible for air escape meansto be provided on/in the diaphragm as indicated. Preferably this escapepassage is provided by a recess and preferably a small groove or channelor other airflow control enhancing feature on or in its surface facingsaid diaphragm to compensate, in use, for falling pressure in the cuffand enable the deflation rate to be controlled. The groove is preferablyelongate and diametrical and central and of differing cross-sectionalarea, largest in the centre of the platen and reducing to zero nearer tothe edge of the platen. Preferably the disc or platen has a flatnormally lower surface in which the groove is also located and the rootof the groove is curved. Instead of an elongate groove, a recess ofother shape may be provided. Other airflow control enhancing featurespreferably additionally or alternatively include the surface finish ofthe platen and/or the diaphragm and/or the shape of both parts and/orthe softness and/or thickness of the diaphragm.

Thus in its broadest aspect here compensating means are provided toenable the restriction or opening of the path between the diaphragm andplaten to achieve a compensating affect using the changing curvature ofthe diaphragm and thus may be by way of the means indicated above e.g.by forming on the platen and/or diaphragm.

When the valve is closed, this exhaust hole or port is sealed orsubstantially closed by the disc or platen, which is held down by meansextending from the release means which is preferably an axiallydisplaceable rotary knob secured with a fine screw thread to the valvebody or a non-axially displaceable rotary knob having a cam which actson lever means to achieve the same effect. When the release means is insuch position, the pressure in the cuff and monitor can be raised bypumping the inflation means typically to above systolic pressure. Therelationship between the platen and diaphragm is preferred such thatreleasing the release means slightly, allows the platen to rise and aircan seep from (the high pressure area) of the valve/chamber thereonthrough the port in the diaphragm and between the face of the platen anddiaphragm to atmosphere to allow the pressure of the cuff and monitor todrop. Adjusting the release means, normally by rotation, to open andclosed positions or intermediate positions controls the rate at whichair flows through the valve.

It is to be appreciated that an air passage is created between thediaphragm and platen which varies in size depending on the pressure onthe diaphragm (and unlike the mentioned U.S. prior art, not solelydependent on the deformation of the hole in the diaphragm). The grooveis formed in the platen as an open channel of varying/differingcross-section and which is partially closed by contact with thediaphragm. The amount of groove sealed by the diaphragm is desirablycontrolled by the curvature of the diaphragm (created by the cuffpressure) and the position of the platen. Altering the position of theplaten allows the flow rate through the valve to be adjusted fordifferent cuff and arm sizes. The preferably elastomeric diaphragm andthe platen are such that the diaphragm will, if not constrained by theplaten, lift (be deformed) by the cuff air pressure. If the cuff ispressurized and the platen is raised, the diaphragm will tend to followthe platen, closing the air passage formed in the groove between thediaphragm and the platen by an amount proportional to the differencebetween the cuff pressure and atmospheric pressure. As the pressure inthe cuff drops, the diaphragm will deform less, exposing more of thegroove formed in the platen to atmosphere and opening the air passageformed in the groove between the platen and diaphragm, slightly andcompensating for the falling pressure in the cuff. The screw action andthe cam arrangement embodiments give the clinician a familiar action, aproportional response—more rotation, more flow—allowing the flow rate tobe adjusted as required. Pressure compensation matches the chosen flowrate. The clinician can stop the flow or open it partially or fully. Thecomponents are also easy to mould—an open slot rather than a fine hole.The advantages of the valve of the present invention resides in itsgreat simplicity, and enables the valve to be shut off or fully openedand to have one knob that controls everything.

Click or pawl and ratchet means associated with the release meansregulate the movement of the control knob and provide audible and/orphysical feedback to the clinician.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described further by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a side elevation of a first embodiment of a control valve ofthe present invention;

FIG. 1A is an end elevation of the valve of FIG. 1;

FIG. 1B is a perspective view from below of the control knob of FIGS. 1,1A or 4;

FIG. 1C is a perspective view of a click spring;

FIG. 2 is an exploded perspective view of the components of the deviceof FIGS. 1, 1A and 4;

FIG. 3 is a perspective view of the underside of the preferredconstruction of the control disc or closure platen for use in theembodiments of FIGS. 1, 1A and 2 and 4 or FIGS. 5 to 15;

FIG. 4 is a cross section on the line A-A of FIG. 1A through thedeflation control valve with rotary knob adjustment and shown partlyconnected downstream to a squeeze-bulb;

FIG. 5 is a perspective view of a second deflation control valve forminga preferred embodiment of the invention;

FIG. 6 is an exploded perspective view of the valve of FIG. 5;

FIG. 6A is a longitudinal cross section through the valve of FIGS. 5 and6;

FIG. 6B is a transverse section through the valve of FIGS. 5 and 6;

FIG. 7 is a perspective view from the cuff attachment and of the valveof FIGS. 5 and 6 but without the inflation bulb and without the bodyhalves and showing the cam in the maximum displacing and valve travelingposition (the knob is in the fully closed position);

FIG. 8 is a view similar to FIG. 7 with the knob raised;

FIGS. 9 and 10 are reversed plan and perspective views from below of thepart of the valve of FIGS. 7 and 8 but turned through 180° and withoutbody halves (20 a, 20 b) still in the maximum lever displacement by thecontrol of the rotary knob;

FIGS. 11 and 12 are similar views to FIGS. 9 and 10 but at anintermediate position of adjustment;

FIGS. 13 and 14 are opposite end views of the valve in the position asshown in FIGS. 11 and 12; and

FIG. 15 is a perspective view from below the components shown in thecondition of FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A rubber squeeze-bulb 1 (only shown in part but similar to bulb 12 inFIGS. 5 and 6) is provided for inflating a cuff (not shown) of asphygmomanometer and is provided in known manner with an inlet apertureat one end for receiving a one-way inlet valve (not shown). At theopposite end outlet side of bulb 1 there is an outlet sleeve portion 1Asealed around a one way rubber valve or check valve 2 contained in aninlet of a valve body 3. The inlet of body 3 leads into the valvechamber formed by the valve body 3 having a tubular upper portionforming a seat for a flexible valve member or diaphragm 4. An outlet 3Aleads to the cuff. Elastomeric disc-like diaphragm 4 (about 45 shore Amaterial), is seated in the body 3 and sealed at its periphery againstthe seat by means of a sealing cap 6 including an externally threadedtubular portion which is threadingly engaged and secured in an upperportion of valve body 3 and urges the diaphragm 4 into sealingengagement with its seat. The cap 6 has a central aperture 6A forexhaust of air from the valve when opened and to enable a pin or boss toextend therethrough to act on the diaphragm 4 via a disc or platen.Diaphragm 4 has a central passage or hole or port 4A for flow of airwhich is controlled/stopped via a disc like platen 5. A rotary controlknob 8 is provided threadingly mounted on valve body 3 which has a finethread and axially displaceable by rotation to move towards and awayfrom the platen 5. Knob 8 has a platen engagement pin or boss 8A on itslower inner side forming a control portion of the knob as it extendsthrough aperture 6A in cap 6 and may bear against the upper surface ofplaten 5. A metal click spring 7 is mounted on the top of cap 6 on tworetaining pins 6A, 6B extending through spring holes 7B and the knob 8has a circle of serrations on its inner side engageable by a pawlportion 7C of spring 7. Click spring 7 and in particular pawl or dimpleportion 7C operates against the ridges or serrations 8B on the undersideof the knob 8. Spring 7 comprises two spaced apart flap-like portions 7Dlying in the same plane and from which, in its position of use, twoyoke-like springs arm portions 7E extend inclinedly downwardly to twospaced apart flat web-like mounting portions 7F both lying in the sameplane and in which holes 7B are found. The small dimple 7D on oneportion runs against the cap serrations 8B to create the click action.The other portion 7D also runs against the cap surface but on a smoothsection inboard of the serrations. The spring 7 pivots against the clampon the portion 7F of its surface with the two holes 7B and the cap 6presses against both the bottom and top legs of the spring, ensuring thespring dimple clicks against the cap serrations. The platen/lever/camassembly have the capability of closing the valve completely.

Air from the atmosphere is pumped into and through the valve body 3 bythe rubber bulb 1, entering through the one way valve 2. The outlet ofthe body 3 has a rubber tube 3A running to the manometer and cuff.Diaphragm 4 is sealed to valve body 3 around its periphery by cap 6.There is a second outlet from valve body 3 via the port 4A in the centreof diaphragm 4 for exhausting/deflating the cuff. When the valve isclosed, this exhaust hole or port 4A is sealed or substantially closedby platen 5, which is held down by the boss 8A on knob 8 which securedwith a fine screw thread to valve body 3. When knob 8 is screwed closed(down), the pressure in the cuff and monitor can be raised by pumpingbulb 1, typically to above systolic pressure. Unscrewing knob 8 slightlyallows platen 5 to rise. Air can seep from valve body 3 (the highpressure area) through port 4A, along the passage formed by the groovein the platen, between the face of platen 5 and diaphragm 4 and througha hole in the knob 8, or otherwise to atmosphere, allowing the pressurein the cuff and monitor to drop. Opening and closing knob 8 controls therate at which air flows through the valve.

A second effect provides pressure compensation. The underside ofdiaphragm 4 is subject to cuff pressure. The elastomeric diaphragm 4will, if not constrained by the platen, lift (be deformed) by thispressure. If the cuff is pressurized and the platen 5 is raised, thediaphragm will tend to follow the platen, exposing the groove formed inthe platen that connects port 4A to atmosphere by an amount proportionalto the difference between the cuff pressure and atmosphere. As thepressure in the cuff drops, the diaphragm will deform less, increasingthe size of the air passage leading from port 4A via the platen grooveto atmosphere by exposing a section of the groove in the platen with awider cross-sectional area. This effect, if correctly exploited, willcompensate for the falling pressure in the cuff and mean that aclinician, once the correct flow rate has been achieved, will not haveto continue to adjust the valve as the pressure drops.

It has been discovered that this effect is influenced by the surfacefinish of the platen and diaphragm, the shape of both parts and thesoftness of the diaphragm. Difficulties can be experienced achieving aprecise control of the deflation rate and compensate for pressureeffectively using a flat diaphragm and platen. The valve may tend eithernot to compensate enough for pressure (operate like a needle valve) orto overcompensate and increase flow rate dramatically as the pressuredropped. It has been discovered that adding a small groove to the faceof the platen overcomes these difficulties and makes the compensationwork well and the airflow control accurate and provides a preferredembodiment. The groove is at its deepest and widest over port 4A andtapers to nothing about 5 mm either side of port 4A.

The amount of the groove revealed by the diaphragm defines the size ofthe gap through which air can flow, the more the diaphragm bulges, themore of the platen face it covers and the smaller the passage for air toflow through. This additional feature is easily mouldable and makes thepressure compensation and flow control much more reliable and precise.Good compensation can be achieved by choosing the correct grooveprofile, diaphragm material, thickness and texture and overall geometry.

One of the characteristics of a face valve is that very small movementsof the platen can have a large effect on airflow. The elasticity of thediaphragm and the application of pressure to most of its under surface(causing it to bulge under pressure) increase the amount of movementneeded to change the air flow rate. The provision of a groove or slothelps further. It is desirable that the screw thread should have sometolerance, and gripping the knob in different ways can alsosignificantly affect the flow rate through the valve. A screw threadgives a linear relationship between the rotation of the knob and itsaxial movement. This is not helpful when designing one valve to copewith different cuff and patient sizes—much more air needs to flow from alarge cuff on a large patient than a small cuff on a child to deliverthe same deflation rate. Nor does the clinician want to turn the knob 8far to shut off or fully open the valve (both actions are needed duringa blood pressure test).

A second and preferred embodiment of deflection control valve 10 isillustrated in FIGS. 3 and 5 to 15 wherein a known rubber squeezeinflation bulb 12 is provided with inlet check valve 12A at its inletend and connected at its outlet end via check valve 11 to the inletportion of the valve body 13 which has knob-mounting spindle 13Aextending from the top thereof and, like in FIG. 4, defines a seat in achamber on one side of its air through-flow passage and on which seat adiaphragm 24 is clamped by means of a clamp 16 which snap-fits onto thebody 13 sealing the diaphragm 14 against the seat.

Diaphragm 14 has a central aperture or port 14A similar to thatdescribed previously and communicates the through-flow passage with theupper side of the diaphragm from whence air under pressure may escape toatmosphere. A disc or platen 15 is provided identical or similar toplaten 5 described previously with a double tapered groove 15A part wayalong its diameter as described previously. Platen 15 is releasablyurgeable against diaphragm 14 to close or partially close aperture 14Aby means of a lever 19 which has an annular or ring-like portion 19A onwhich a cam 18A of raising knob 18 may slidingly act, and has aplate-like portion 19B which is displaceable in aperture 16A of clamp 16to act on platen 15. Lever 19 is a pivotally mounted at 19B on clamp 16.Clamp 16 has diametrically opposite recesses 16B, 16C in which flanges13A, 13B of the valve body 13 locate to prevent relative rotation. Twoclam shells on upper and lower cases 20A, 20B, clamp together and holdknob 18 rotatable on spindle 13A.

The disk or platen 15 (identical or similar to platen 5 describedpreviously) is controlled by the action of the cam 18A on the face ofthe knob 18 which is rotatable on spindle 13A. This cam 18A ispreferably shaped so that the valve behaves to the user in an apparentlylinear way in the adjustment zone, does not have to be turned much morefor large cuffs than for small, or to reach closed and fully openstates. Placing the knob on the opposite side of the valve the platen 15and the diaphragm 14 brings a number of advantages. Mechanical advantagecan be built into the lever 19 that transmits the cam 18A movement tothe face of the platen 15, so that there is more travel at the knob cam18A than at the platen 15—this helps reduce the effect of knob bearingtolerance and any sideways movements of the knob caused by theclinicians holding the valve in unexpected ways.

Any axial movement of the knob which is more difficult to control doesnot affect the position of the lever or platen. The knob bearing shaftor spindle 13A is mounted directly to the back of top face of the valvebody and is provided with rotation stops 13E, and knob 8 is locatedaxially between abutment surfaces on the valve body and on the inside ofcase 20B so that the knob can be handled reasonably roughly withoutapplying forces to the valve mechanism. A click action (click 17A andmetal click spring 17B operating on knob ridges 8B) can also beassembled easily in such a way that the forces generated by the spring17B and click 17A do not affect the position of the lever 19 or platen15. The diaphragm 14 is sealed to the body with snap-fit clamp 16. Clamp16 also provides a pivot 19B & C for lever 19 and pivot 17AA for click17A. The two body halves 20A and 20B, protect the mechanics of thevalve.

The rotary knob 18 turns freely on the spindle 13A (throughapproximately 310° as controlled by stop 13E (FIG. 8). The cam isradially tapered and moves lever 19 which acts on the platen 15 andtherefore on diaphragm 14. Lever 19 pivots in bearing holes 19B & C inclamp 16. The platen 15 is not sealingly mounted to the valve body. Thediaphragm 14 is sealed to the body by a periphery at edge of clamp 16,which snaps onto the body 13. Air cannot escape from the valve bodythrough hole 14A in the diaphragm to atmosphere when the diaphragm ispressed flat against the valve body by the platen (the platen is forcedagainst the diaphragm by the lever 19 and knob cam 18A). The diaphragm14 seals against the platen 15 around the periphery of the platen (not aparticularly good seal) and also against the spigot 13F formed in thecentre of the valve body (which contacts the raised annular wall 14B onthe diaphragm 14—this thin wall 14B reduces the force needed to seal thediaphragm and reduces the likelihood of parts creeping over time if thevalve is left tight shut for long periods).

When the knob 18 is turned and the platen 15 allowed to lift away fromthe valve body, the pressure in the valve flexes the diaphragm 14 andlifts the platen 15. The diaphragm 14 flexes at its centre (it is heldaround its periphery), and an escape path is created for the pressurizedair in the valve body past the thin sealing rib on the diaphragm and thevalve spigot, through the hole in the centre of the diaphragm, down thetwo passages formed between the platen groove and the diaphragm and, ifthe curvature of the diaphragm is sufficient, to atmosphere. The morethe diaphragm is curved (flexed), the more of the ends of the platengroove are revealed and the larger the air escape path cross sectionbecomes. The diaphragm curvature depends on the position of the platen(controlled by the cam and lever) and on the pressure drop across thediaphragm (as mentioned previously, the higher the pressure in thevalve, the greater the diaphragm deflection, the more the platen grooveis covered, the smaller the air escape orifice—hence pressurecompensation).

Whilst there is axial movement of the knob in the first embodiment thereis no movement along the axis of rotation in this second embodimentmerely about said axis. Thus it is possible to have whatever desiredrelationship between the knob rotation and platen movement thereof, (ifneed not be linear, and can be adjusted so that the relationship betweenthe knob rotation and deflation rate (rather than platen movement)appears linear to the user). The knob bearing is easy to form, the knobcan be robust, the delicate mechanics of the valve protected and atactile ‘click’ is provided.

The click action of the tactile means is created here by a flat spring,trapped at its centre on the valve body (the post-like moulding 13Dlocates the click spring) driving the plastic pawl 17C (called theclick) against serrations or ridges 188. The pawl 17C is pivoted on theclamp 16 to prevent any sideways movement. The reason for using aplastic pawl 17C (rather than simply having a detail on the spring thatengages on the ridges 18B on the underside of the knob 18) is to controlthe feel of the click with greater accuracy—these clicks happen every 6°of knob rotation, which is a small movement to identify with the click.The shape of the ridges on the underside of the knob and theco-operating boss on the face of the plastic pawl or ‘click’ componentcreate the feel. The ridges do not cover all the rotation of theknob—they define the ‘working zone’.

Taking the knob zero point (cam point 18C against 19A) as being when thevalve is fully shut off, the first click is felt after 48° of rotation.With the smallest cuff size used on a child, the correct deflation ratefor reading systolic or diastolic blood pressure will be reached afterabout 6 clicks, or a further 36° rotation (at normal room temperature).The knob is turned a further 15 or so clicks (approximately 90°) todeflate the cuff reasonably fast between measuring points. The correctdeflation rate for measuring the blood pressure of an obese adult isreached about 15-20 clicks in (rather than 6 for a child). A total of 38clicks (or 228° of rotation) has been provided, so that a clinicianshould in most cases be working within the ‘click’ zone while takingpressure readings and moving between measuring points. Once the bloodpressure has been measured, the valve is opened fully to give thequickest deflation. The valve is fully open (18D adjacent 19A) when theknob is rotated 310° from the zero (or closed) position and the last 34°of valve movement have no clicks. One stop for knob rotation isprovided—it can be seen on the valve body on the bulb side of the knobspindle 13A and there is a corresponding rib 18E on the underside of theknob.

Thus in summary, the present invention provides an adjustable face valveconnectable to a pressurisable cuff or other vessel to control air flowfrom the cuff, preferably with pressure compensation such that valveautomatically maintains a constant rate of pressure change in the cufffor a given setting of the valve regardless of the pressure in the cuff,the main reason for pressure compensation being to provide the clinicianwith a valve that does not need to be adjusted as the pressure in thecuff falls. The advantages of driving the platen with a cam, other thanthe mechanical and structural advantages of the cam arrangement we havearrived at (mechanical advantage, minimal disturbance of the platenposition if the user applies pressure to the knob while holding it,disconnection of the more delicate parts of the valve from the user sothat they cannot be abused easily), include making the relationshipbetween knob rotation and deflation rate more intuitive to the user—moreproportional, which means that the cam profile has to be slightlyunusual such that it has a shut off ramp operating to close the valve,which reduces to a very gradual spiral angle at the beginning of thedeflation zone (for controlling small cuffs). The spiral angle thenincreases as the valve is opened further for controlling larger cuffs orquick exhaust.

It is intended the technique of and valve for controlling small air flowwith pressure compensation, has applications other than forsphygmomanometers.

1. A deflation control valve that automatically varies the rate of airflow through said control valve to provide a constant but adjustablerate of change of pressure during the deflation or exhaust of gas heldin a closed pressurisable vessel to which said valve is connectablecomprising a valve body having a passage communicatable with saidpressurisable vessel, said valve body defining a valve chambercommunicating with said passage in which a flexible diaphragm isprovided partially or substantially closing said valve chamber, saiddiaphragm being in sealing abutment with a seat in said valve housingaround the periphery of said diaphragm, and forming on the opposing sidea part of an exhaust chamber, said diaphragm, in use, being, on thevalve chamber side subject to the gas pressure in said pressurisablevessel and, on the opposing side, subject to the gas pressure in theexhaust chamber, which may be atmospheric pressure, and said diaphragmhaving an aperture or port extending therethrough, and said diaphragm onone side being in communication with said valve chamber and, on theopposite side, being in communication with said exhaust chamber oratmosphere and being closeable or partially closeable by a displaceableclosure disc, plate or platen which is releasably held in the closingposition against said diaphragm and covering said port by an operable,controllable or adjustable release means, which by adjusting saidrelease means to open and closed positions or intermediate positions,controls the rate at which gas flows through the valve, gas passing fromthe valve chamber through the port in the diaphragm and between the faceof the closure disc and diaphragm to exhaust or atmosphere to allow thepressure of the pressure chamber to drop in a controlled manner.
 2. Avalve as claimed in claim 1, where the resistance to the passage of gasfrom the higher pressure in said valve chamber to the lower pressure insaid exhaust chamber is determined by the surface area of said diaphragmin contact with said closure disc, the local contact pressure betweensaid diaphragm and said closure disc and the material, geometry andsurface finish of said diaphragm and said closure disc.
 3. A valve asclaimed in claims 1 and 2, such that, on releasing the release meansslightly, the closure disc moves away from the diaphragm, the pressuredifference between the higher pressure in the valve chamber and thelower pressure in the exhaust chamber urges said flexible diaphragmtowards said closure disc, creating a curvature in said diaphragm suchthat the surface area of said diaphragm in contact with said closuredisc and the local contact pressure between said diaphragm and saidclosure disc controls the rate at which gas can seep from the higherpressure area in the valve chamber through the port in the diaphragm tothe lower pressure area in the exhaust chamber in a manner that isdependent on the position of the closure disc in relation to thediaphragm, the pressure difference between the higher and lower pressureareas and the nature of the materials, surface finishes and form of thediaphragm and closure disc, such that the valve automatically maintainsa constant rate of pressure change in the pressurisable vessel as thepressure difference between the valve chamber and the exhaust chamberchanges due to loss of gas from the pressurisable vessel.
 4. A valve asclaimed in claim 1, 2 and 3, in which a manually operable release meansis a reversibly rotatable and axially displaceable control knob bearableon the platen.
 5. A valve as claimed in 1, 2 and 3, in which a manuallyoperable release means is a non-axially displaceable rotary knob withcam and lever means for reversibly urging the platen into a closingposition, the cam so formed that there appears to the user to be alinearly (or any other) proportional relationship between the angularposition of the knob and the rate of change of pressure differencebetween the valve chamber and the exhaust chamber.
 6. A valve as claimedin claim 5, in which the displacement means associated with the knob andis such that the movement is amplified and thus greater movement of theknob enables a smaller movement of the disc or platen.
 7. A valve asclaimed in any of claims 1 to 6, in which the closure disc and/ordiaphragm has an air escape passage or means which varies incross-section as the deformation of the diaphragm due to the pressuredifference across it and the position (lifting and lowering) of theclosure disc varies.
 8. A valve as claimed in claim 7, wherein alternateair escape control means is provided on or in the diaphragm tocompensate for falling pressure in the pressurisable vessel.
 9. A valveas claimed in claim 7 or 8, in which the air escape means is an escapepassage in the form of a recess to compensate, in use, for fallingpressure in the pressure chamber and enable the rate of change ofpressure in the valve chamber to be controlled.
 10. A valve as claimedin claim 7, wherein alternate air escape control means is provided on orin the closure disc to compensate for falling pressure in thepressurisable vessel.
 11. A valve as claimed in claim 8, in which thealternate air escape means is a small groove or channel or other airflowcontrol enhancing feature on or in the surface of said diaphragm facingsaid closure disc.
 12. A valve as claimed in claim 10, in which thealternate air escape means is a small groove or channel, or a projection(such as a ridge or bump) or other airflow control enhancing feature onor in the surface of said closure disc facing said diaphragm.
 13. Avalve as claimed in claim 11, in which the groove is elongate anddiametrical and central and positioned over or through the portperforating the diaphragm and of a varying/differing cross-sectionalarea, largest in the centre of either the closure disc or the diaphragmand reducing to zero nearer to the edge of the closure disc ordiaphragm, such that amount of surface area of the diaphragm in contactwith the closure disc determines the minimum cross-sectional area of thegroove through which gas escaping from the higher pressure chamber tothe exhaust chamber has to flow.
 14. A valve as claimed in any of claims1 to 13, in which the airflow control enhancing features are providedadditionally or alternatively including the surface finish of theclosure disc and/or the diaphragm and/or the shape of both parts and/orthe softness and/or thickness of the diaphragm.
 15. A valve as claimedin any of claims 1 to 14, in which, in use, when the valve is closed,the diaphragm port is sealed or substantially closed by the closure discor platen, which is held down by means extending from the release means.16. A valve is claimed in claim 15, in which the release means is anaxially displaceable rotary knob secured with a fine screw thread to thevalve body or a non-axially displaceable rotary knob having a cam whichacts on lever means to achieve the same effect.
 17. A valve as claimedin any of claims 1 to 16, in which click or pawl and ratchet means areassociated with the release means and regulate the movement of thecontrol knob and provide audible and/or physical feedback to theclinician.
 18. A deflation control valve substantially as hereindescribed with reference to the accompanying drawings.
 19. A deflationcontrol valve as claimed in any of claims 1 to 18 in combination with asphygmomanometer.
 20. A deflation control valve in the form of a facevalve for a sphygmomanometer comprising a valve body having a firstoutlet passage connectable to be communicatable with a pressurisabletube connected to a cuff of a sphygmomanometer, and an inlet passageconnectable to a rubber bulb pump or like inflation means, said valvebody defining a valve chamber in which a flexible diaphragm is providedpartially or substantially closing the chamber and said diaphragm havinga deflation, air-flow passage which on one side of the diaphragm is incommunication with said inlet and outlet passage and, on the oppositeside of the diaphragm, is in communication with an exhaust outlet oratmosphere and is closeable or partially closeable during inflation by adisplaceable closure disc, plate or platen which is releasably held inthe closing position against said passage by a manually operable,controllable or adjustable release means.